#include <bits/stdc++.h>
using namespace std;
int n,m,k;
const int N=5e5+10;
int vis[N],dis[N];
vector<int>v[N],ans;
void dfs(int x){
    if(vis[x])return;
    vis[x]=1;
    for(auto y:v[x]){
        if(vis[y]) continue;
        dfs(y);
        dis[x]=max(dis[x],dis[y]+1);
    }
    if(dis[x]>=k || x==1){
        ans.push_back(x);
        dis[x]=-1;
    }
}
void solve(){
    cin>>n>>m;
    k=ceil(sqrt(n));
    ans.clear();
    for(int i=1;i<=m;i++){
        int x,y;cin>>x>>y;
        v[x].push_back(y);
        v[y].push_back(x);
    }
    dfs(1);
    cout<<ans.size()<<endl;
    for(auto x:ans) cout<<x<<" ";cout<<endl;
    for(int i=1;i<=n;i++) vis[i]=dis[i]=0,v[i].clear();    
}

int main(){
    int  t;
    cin>>t;
    while(t--){
        solve();
    }
    return 0;
}